Snap action switch with creepaction motor



Aug. 9, 1949.

R. VALVERDE 2,478,344

SNAP ACTION SWITCH WITH CREEP-ACTION MOTOR Filed May 9, 1946 Patented Aug. 9, 1949 UNITED STATES PATENT OFFICE SNAP ACTION SWITCH WITH CREEP- ACTION MOTOR Robert .Valverde, New York, N. Y. Application May 9,1946, Serial No. 668,413

" '2 Claims.

The switch of this invention obtains 'snapaction even though operated by a creep-action motor; and the invention. isparticularly suited to thermostats which'are operated by strips of bimetal. When applied to the thermostat of an electric iron, this invention reaches the adjusted temperature in practically one step; responds rapidly to temperature changes in the soleplate; has a small differential; is .free from cycling; is

not damaged by mechanical vibration; and has a capacity of 1.5 kilowatts at 120 volts direct cur-' rent.

Figure 1 shows the invention embodied in a thermostat as part of an electric iron. v

Figure 2 shows an enlarged view of the thermostat as part of the soleplate.

Figure 3 shows the contact end; view of the thermostat as part of the soleplate.

In Fig. 1 a sadiron soleplate I has cast in ita cavity 2 into which is bowed an Invar strip 3. Cavity 2 with bowed strip 3 comprise my thermal motor; and they, combined with my thermal switch 4, and adjusting knob 5, comprise my thermostat. Switch t is mounted on the edge 6 of the cavity 2. Invar strip 3 is preferably mounted on the median line Tof the soleplate.

In Figs, 2 and 3, contact, arm 8 and backstop 9 are electrically insulated from and mounted. on the Invar strip 3 at the quarter point where a tension screw l adjusts the pressure of the free (left-hand) end of contact arm 3 against backstop 9. To the free end of contact arm 8 there is riveted an armature l2 with a silver contact strip 13. The contact l3 bears against a fixed contact M which is a silver strip binding a magnet IE to a plate [6. Magnet I5 is electrically insulated from contact M and plate l6, which latter are electrically connected. The plate [-6 is connected to a spiral spring I! which is preferably an integral part of the plate H5. The outer end of the spring I1 is mounted on frame l8 by means of a twin eyelet I 9 which is insulated from the frame I8 by layers of insulating materials. The opening through the eyelet I9 is threaded and a terminal screw l9 screws into the eyelet l 9.

The contact arm 8 and backstop 9 are secured at their right-hand ends to a twin eyelet into which a screw is threaded. The eyelet 20 passes also through the Invar strip 3 but is insulated from the strip 3. Screws [9 and 20' are the electric terminals of my switch.

The position of fixed contact [4 for temperature adjustment is determined by a feed screw 2| threaded through a nut 22 on the frame l8.

Feed screw 2| is insulated an insulating washer 23.

The top of feed screw 2! is integral with a shaft 24 which is slidably keyed to a temperature adjustment knob 25. Knob 25 is positioned on shell 26 by plate 2? and turns freely. Knob 25 projects through plastic handle 28 for thumb adjustment of ironing temperatures. The end of shaft 24 is splined to slide in spline 30 moulded into plastic knob 25 to permit keying marks Oif, Rayon, Silk, Wool, Cotton, Linen on'knob 25 to arrow mark 29, Fig. 1, moulded into plastic handle 28, at the adjusted soleplate temperatures. Cord 3| electrically connects the current supply to the series connected heater element and my thermostat in a conventional manner.

For causing the contact M to move up when the knob 5 is adjusted, a clip 34 is attached to the magnet by means of turned-over edges of the clip which engage in notches 35 in the side of the magnet. The clip 34 extends across the top of the magnet under the layer of insulation that separates the magnet from the plate It. A pin 37 extends through a hole in the center portion of the clip 34 and extends upward through an axial bore in the screw 21 and shaft 2 to a cross bore 38. The upper end of the pin 31 is bent over in the cross bore 38, as best shown in Figure 2, to prevent the pin from pulling downward.

A recess or groove is provided in the top of the magnet l5 for receiving the head of the screw 3'1, and this head is substantially larger than the opening in the clip 34 so that the pin 31 serves, in effect, as a rivet for securing the magnet assembly, including the contact [4, to the adjusting screw 2 I.

Operation-In the Off position of knob 25 the fixed contact I 4 presses against the insulated feed screw button 23 and the contacts 13 and I 4 are separated. Turning knob to Rayon advances the feed screw 2|, slides the shaft 24 in its spline 30 and contacts l3 and I4 close. Soleplate l heats up, cavity 2 lengthens, strip 3 does not lengthen but the bow flattens and contact arm 8 and backstop 9 lower and with lever action release pressure on the contacts. But the contacts do not separate because armature I2 is magnetically attracted by the poles of magnet [5. Further flattening of Invar strip 3 causes backstop 9 to draw away from the springy contact arm 8 until the tension in the contact arm exceeds the magnetic pull. The contacts then separate with a snap and the direct current are is promptly quenched by the increasing magnetic lines of force from pole from the plate I6 by to pole at right angles to Hence the contacts are not damaged.

Out of the stronger part of the magnetic field, the armature l2 can now press firmly against the solid backstop 9. Backstop 9 limits the opening motion of the contact and the stifiness of contact arm 8 adjusted to a maximum for snap action by tension screw H, controls the sensitivity of the thermostat. External vibration of ironing has no effect on the contact arm to cause false contacting. As the soleplate cools the armature 1'2 is rapidly brought back into the stronger magnetic field and the contacts l3 and 14 close with a snap and without bouncing. Tension screw ll adjusts the pressure so that contact arm 8 does not leave backstop 9 until the contacts are a minimum distance apart for eflicient arc quenching. Hence on contact openin the separation is a minimum and so is the diiferential. Also the direct response of the contacts to a change in length of the cavity results in a minimum differential. The design of my thermostat is such that only the cavity, in effect, expands with heat. The other parts made of Invar either do not expand with heat or they compensate each other. Hence the effect of different parts of my thermostat being at different temperatures at different times during temperature adjustment and balance is negligible. The electric iron heats up to the adjusted temperature without stepping. Since the contact arm is never swinging free, my thermostat is free from cycling. The permanent magnet in my thermostat uniquely performs two functions; snap action and magnetic blowout. This is the more efiective in that the magnet is electrically insulated from the arc. At electric iron temperatures the magnet shows no deterioration. The efiiciency of my thermostat is shown by lack of appreciable contact wear in life tests as an electric iron operating on direct current.

The preferred embodiment of the invention has been described, but changes and modifications can be made, and the invention can be used with various switches as defined in the claims.

I claim as my invention:

1. A thermal switch comprising a movable contact assembly including a contact, an armature the incipient arc. overheated and 4 connected with the contact, and a spring arm by which the armature and movable contact are carried, a relatively fixed contact, a permanent magnet electrically insulated from the contacts and in position to attract the armature and provide both snap action and are blowout at the contacts, backstop behind the movable contact assembly and bearing against said assembly to hold the switch contacts closed at low temperature, and thermal-responsive means that operates with temperature rise to stress the spring arm and urge the contacts apart, and to move the backstop away from the movable contact assembly for a limited distance less than the effective range of action of the spring arm so that the backstop is in the path of the movable contact assembly when the switch opens with its snap action;

2. In a switch that is operated by a creepaction motor, a movable contact assembly including a contact, an armature connected with the contact and a spring arm by which the armature and movable contact are carried, a relatively fixed contact, a permanent magnet electrically insulated from the contacts and in. position to.

attract the armature and provide both snap action and are blowout at the contacts, a backstop behind the movable contact assembly, and a creep-action motor that stresses the spring arm to urge the contacts apart, said back stop being located in the path of the movable contact assembly and at a distance from the assembly less than the efiective range of action of the spring arm while stressed by the movement of the creepaction motor.

ROBERT VALVERDE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,024,856 Graham Dec. 17, 1935 2,096,502 Wetzel Oct. 19, 1937 2,183,469 Sparklin Dec. 12, 1939 2,248,666 Fischer July 8, 1941 2,389,686 Reingruber et a1. Nov. 27, 1945 

